This invention relates generally to angiography and/or particularly to an improved catheter for injecting medical fluids such as radiographic contrast fluid into living organisms.
Angiography is a procedure used in the treatment of cardiovascular conditions including abnormalities or restrictions in blood vessels of a human or animal body. During angiography, a radiographic contrast material is injected through a catheter into a vein or artery, which then passes to vascular structures in fluid communication with the vein or artery. When X-rays are passed through the region of the body into which the contrast material is injected, they are absorbed by the contrast material, providing radiographic images of the desired vascular structure(s). The images can be recorded on film or video tape and/or displayed on a fluoroscope monitor. The images can be used for many purposes, as for example diagnostics, and for operative procedures such as angioplasty, wherein a balloon is inserted into a vascular system and inflated to open a stenosis.
The contrast material can be injected into the catheter by either manual or automated injection systems. Although the apparatus for injecting the contrast material can vary, many current systems include a syringe operatively connected with the catheter. The syringe has a chamber for holding the contrast material and a plunger reciprocally moveable within the chamber. An example of one such apparatus is U.S. Pat. No. 5,573,515, the entire disclosure of which is incorporated herein by reference. In this apparatus, the contrast material is suctioned into the chamber when the plunger is moved to create a partial vacuum within the chamber. A reversal of the plunger direction first forces air out of the chamber and then delivers the contrast material to the catheter at a rate and volume determined by the speed of movement of the plunger.
In a manual system the user or operator loads the syringe and ejects air from the chamber before connecting the syringe to the catheter. The user of a manual system adjusts the rate and volume of injection by altering the manual force applied to the plunger. The maximum injection pressure for manual systems is typically limited to 200 p.s.i. (i.e. the maximum pressure that can be applied by the human hand), and the maximum quantity of fluid is about 12 cc.
Angiography can include the injection of fluids other than the contrast material. For example, a saline flush and/or the injection of fluid medications may be desired.
The catheter through which the contrast agent or other fluid is supplied is typically inserted percutaneously and into the desired artery or vein. When inserted percutaneously, a puncture hole is created in both the skin and blood vessel wall at the insertion point in order to correctly position the catheter. It is preferable to use a puncture hole that is as small as possible, to avoid leakage around the catheter and to minimize the subsequent wound size. Additionally, the larger the puncture hole, the greater the opportunity for complications and the more time needed to stop the bleeding after the catheter is removed.
Many presently available catheters have a fixed size (diameter) that extends the entire length of the catheter. Resistance to fluid flow in the catheter is determined by the inside diameter. Therefore, the size of catheter chosen for a specific procedure is based upon the inside diameter needed to achieve the particular flow rates associated with the procedure. However, such fixed diameter catheters have the same outside diameter at the puncture site as at other points on the catheter. As a result of this design, the wound at the puncture site may be unduly large for the particular procedure to be performed.
Although the presently available catheters are well accepted by the medical profession and function as required, it is desirable to have a catheter that minimizes the vascular puncture site diameter, but allows minimal resistance to fluid flow. In other words, it is desirable to provide a catheter that minimizes the trauma to a patient but provides versatility to the user for many varied applications and uses of the catheter.
In view of the foregoing, it is an object of the present invention to overcome the deficiencies of existing catheters.
It is a further object of the present invention to provide a catheter that minimizes the wound size for use of the catheter and yet still provides a wide variety of potential uses.
It is a further object of the present invention to provide a catheter that is economical to produce.
It is a further object of the present invention to provide a method of ensuring adequate fluid flow through a catheter with the smallest diameter patient incision as possible.
The present invention attempts to address these objects and other objects not specifically enumerated herein through the use of a catheter that has an outer surface, a portion of which is compliant and has an adjustable diameter and another portion which is not adjustable, or non-compliant. It further may include a backbone, a compliant and expandable sheath surrounding the backbone, and an outer non-compliant sheath which covers a portion of the expandable sheath. At least a portion of the outer non-compliant sheath is not expandable.
The backbone allows the catheter to retain a predetermined shape for ease of manipulation and placement of the catheter. The outer non-compliant, nonexpandable sheath limits the expansion of the catheter and is positioned at the insertion point into the patient. The adjustable sheath, however, expands. Thus, the catheter retains the narrow insertion point but expands at either side of the insertion point.
The catheter sheath selectively expands to provide an expanded area and a non-expanded area, which expansion may occur either during, or prior to, the injection of a fluid. This selective expansion is advantageous because the puncture hole at the entry site into the patient is minimized.
In a preferred method of inserting the catheter, the flexible catheter tip and body are compressed, folded or otherwise manipulated to be smaller in diameter than the diameter of outer non-compliant sheath. The outer sheath can be inserted through the skin and vascular wall after which the body of the catheter is inserted through the constraining outer sheath. The body is then expanded to the desired size.
In a second embodiment, there may be no discrete inner expandable sheath at the position where the outer non-compliant sheath is located. Instead, the nonexpandable sheath may be integral with the expandable sheath.
In a further embodiment, the backbone can be removable and replaceable with a different backbone in order to provide a different shape to the catheter.
In yet a further embodiment, the outer non-compliant sheath may be expandable on demand, for example by mechanical structures. This option may be desired when a large device, such as an atherectomy catheter, needs to be inserted through the catheter. Alternately, the outer sheath may be replaceable with an outer sheath having a larger diameter.